ok, where were we... quoting from the previous page

#2) 1 bil: Start actual R&D with tethers. I'd love to put one around Earth, then launch a tether to the Moon, then they could start playing catch with a small "ball". We'd learn a ton from a year's worth of experiments like this. After playing catch for a while, we could even practice soft-landing the ball on the Moon & picking it up again. The round-trip time for the ball would be about a week (I think... I haven't done the math on this one yet) - so the two tethers could even exchange multiple balls in a cosmic juggle! We would also need to practice tossing a payload from the end of the tether to the central tether mass.

This idea is hardly original with me - it is basically wrapping a mission around http://www.tethers.com/papers/CislunarAIAAPaper.pdf

http://www.tethers.com/papers/JPC00MMOSTT.pdf

It is a brilliant idea to explore... getting outside the LOG function in the Rocket Equation is absolutely key to exploration of the inner Solar System for far less fuel/cost/mass than otherwise. Until viable fusion rockets are available (100 years?), this seems like the optimal solution.

One key feasibility question is, how can the Lunar tether restore its orbit? After landing a payload, the tether system has lost some energy. It would be nice if there were a propellant-free way of restoring that energy to the orbit. The Earth tether can run a current through a wire running along a tether, in the opposite direction from the current that would normally be induced by the Earth's magnetic field. In effect, this is pushing against the magnetic field, and would allow the Earth tether to restore its orbit in under 3 months(*2).

The Moon does not have a significant magnetic field, so we don't have this option. If someone on the Moon were able to tie the tether tip to a bucket of rocks immediately after it dropped off a payload, we'd have it made, as this would balance out the momentum. But - we don't have this option either.

The goal would be to turn electrical energy (generated from solar panels at the tether hub) to kinetic energy of the tether. Perhaps this could be done by using a winch to reel the tether in and out as the system rotates - sort of like the way a child pumps up a swing. We need some experimentation here.

Once the tethers are in place, all the miles are free. We could deposit 2500 kg on the Lunar surface for the cost of getting it to LEO.

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Now, the fun part to consider is - if we were really able to deposit 2500 kg on the Lunar surface for (almost) free - what sort of infrastructure could we build up over time? Obviously, this type of capacity could be used to resupply a (nonexistent) Lunar base with food/water - but could we do other things? Here's a list:

1) Tell top American colleges that if they design a rover, we'll park it on the Moon. Solicit proposals, take the top 5, give the top5 schools 200K in development money, and a year later, launch the rovers. We'd have to hitch a ride to LEO & that's it. The only requirements: the rover must be mobile, capable of teleoperation, include a videocamera, and be < 2500 kg.(*2). Total mission cost: $1 mil to develop the rovers, 5 - 50 mil to launch them. We could even partner with a TV network to run a 12 week weekly show, 1 intro, 5 rover builds, 5 rover launch/landings, 1 wrapup. Put it on prime-time, and I'd bet people would watch - plus, it would establish an entertainment link to a real space mission.

2) Set a rover (maybe even one of the above 5) down at the poles, check out the water ice that is almost definitely there.

3) Land a small electric-powered bulldozer/rover near one of the water-ice (?) sites at the poles. Dig a trench. Land a second one, dig more... If the trench were (say) 8 feet deep, 8 feet across, and 30 feet long, it would be suitable for low-tech human occupation. A small dozer or two could dig this, given enough time. If the trench were near the poles, the Sun would never appear overhead - so the trench would be in the shade all the time and we wouldn't need to cover the roof to avoid solar radiation. The dozers could dig until 2/3 of the battery capacity was exhausted, then climb out, maybe climb a small hill, and position themselves for solar recharge - which could take as long as a couple of weeks, but we've got time. When the trench is completed, we could try sending up an inflatable hab that would fit in the trench and be light enough for the tethers to throw. Would this work? No idea! But if it did, it is even possible we could do a quick manned mission with the tethers. Send up some food & water, a couple of space suits, some kind of heater. Send up some scuba air tanks on a separate trip & use them to inflate the hab. Another nice advantage of tethers is that they can be tested repeatedly prior to actual use - obviously, we would take advantage of this prior to anything risky.

An alternative to all of this is landing in a permanently-shadowed crater near the poles - but being in the light (half the time or more) has its advantages.

4) Land a rover near the Apollo 11 landing site, check it out.

5) Sample return - tethers optimize this beautifully.

(6/18/03) Tethers just got some air time on space.com, check out:

http://www.space.com/businesstechnology/technology/tether_tech_030618-1.html

*1: The first referenced PDF file shows 85 days for the tether exactly as defined in the paper. Obviously, if we change key parameters (mass of the system, length of the tether), we change this figure also.

*2: Getting our payload to LEO will cost some, but no more than $20,000,000. Or - as long as we're into tethers - check out http://www.tethers.com/papers/HASTOLAIAAPaper.pdf , we could do it with a high-altitude plane launch.